Transport and relaxation properties of dimethyl sulfoxide-water mixtures at high pressure

The pressure dependence of the deuterium T/sub 1/ in Me/sub 2/SO-D/sub 2/O mixtures and the proton T/sub 1/ and H/sub 2/O self-diffusion coefficients in Me/sub 2/SO-d/sub 6/-H/sub 2/O mixtures has been measured at 25/sup 0/C. The observations of increased motional freedom of H/sub 2/O with the initial application of pressure in mixtures up to 30 wt % Me/sub 2/SO (chi/sub Me/sub 2/SO/ = 0.1) indicates that small amounts of Me/sub 2/SO do not perturb in a major way the overall hydrogen-bond network in H/sub 2/O. The Debye equation describes well the reorientation of water molecules at 1 bar, but it fails at high pressure due to changes in the coupling between rotational and translational motions. The decreased pressure dependence of the rotational-translational coupling in solutions for chi/sub Me/sub 2/SO/ less than or equal to 0.2, as compared to pure water indicates that Me/sub 2/SO enhances the water structure at low Me/sub 2/SO concentration. The pressure dependence of the intramolecular and intermolecular proton dipolar relaxation rates of H/sub 2/O in Me/sub 2/SO-d/sub 6/-H/sub 2/O is also reported. 49 references, 6 figures, 2 tables.